This is a finding with major public health implications because of the growing obesity epidemic. The ramifications are especially pressing in light of new evidence that obese postmenopausal women who experience a fracture are far less likely than nonobese women to be placed on bone-protective medication, said Dr. Compston, professor of bone medicine at the University of Cambridge (England).

She reported on a study of 44,534 postmenopausal women (mean age, 67 years) in the United States and nine other countries who are participating in the ongoing, prospective, observational GLOW (Global Longitudinal Study of Osteoporosis in Women). At enrollment, 23.4% of the women had a body mass index of 30 kg/m

The prevalence of fracture at baseline was 23% in obese women, 24% in nonobese women, and 32% in the underweight study population. The incidence of one or more new fractures during 2 years of follow-up was 6.4% in the obese and similar at 6.8% in the nonobese women, compared with 7.3% in the underweight group.

Thus, nearly one in four postmenopausal women with a fracture is obese. As the obesity rate continues to climb in the developed world, fractures in the obese will increasingly contribute to the overall burden of fractures in the postmenopausal population, Dr. Compston observed.

The higher prevalence and incidence of fracture in underweight postmenopausal women comes as no surprise; low BMI is recognized as a major risk factor for fracture. What was surprising, though, was that only 27% of obese GLOW participants with an incident fracture were placed on bone-protective medication for secondary prevention.

In contrast, the treatment rate in nonobese women with an incident fracture was 41%, and in underweight women it was 57%. The likely explanation for the markedly lower treatment rate in the obese group is the widespread belief that obesity protects against fractures, according to Dr. Compston.

Incident fractures of the ankle and tibia were significantly more common and wrist fractures were less common in obese women, compared with nonobese study participants.

The obese subjects with an incident fracture had significantly higher rates of several comorbid conditions – asthma, emphysema, and type 1 diabetes – than did nonobese women. They also were more likely than nonobese participants with an incident fracture to have a baseline history of two or more falls within the past 2 years. They had more mobility issues as well, as reflected in their increased rate of self-reported need for arm assistance in standing up. It's likely that reduced mobility and increased risk of falling play an important role in the pathogenesis of fractures in obese postmenopausal women, although this is an issue that needs further study, she observed.

In a separate presentation, Helena Johansson presented an analysis of BMI and fracture risk in 281,637 women drawn from 27 prospective, population-based cohort studies that were conducted in more than two dozen countries. The women were aged 20–105 years (mean age, 63 years).

A total of 18,441 osteoporotic fractures occurred in the study population during a mean 4.8 years of follow-up. After adjustment for bone mineral density, obesity proved to be a risk factor for fracture.

For example, women with a BMI of 34 had an adjusted 14% increased risk of osteoporotic fracture, compared with those having a BMI of 26, an elevation in risk that, while modest, was statistically significant.

And women having a BMI of 34 had a more impressive adjusted 60% increased risk of humerus or elbow fracture, added Ms. Johansson, a statistician at the University of Gothenburg (Sweden).

Dr. Compston declared having no relevant financial disclosures. GLOW is supported by grants from Sanofi-Aventis and Warner Chilcott.